The formation of paper from fiber-water slurry involves the drainage of process water on a continuously moving wire screen, dewatering by pressing the wet webs between felts and pressing between a series of heated drums. The rate of paper production depends on how efficiently the water is removed from the webs during this process without affecting the formation or physical properties of the sheets. To achieve this objective water-soluble polymeric chemicals, which are mainly flocculants by nature, are used in the papermaking process. These chemicals are referred to as drainage aids. The drainage aids accelerate or extend the dewatering of pulp during paper and board manufacture.
Because of the decreased availability of natural paper-making pulp and the general move toward recycling waste, the utilization of recycled used paper and ground hard wood pulps for newsprint and other types of paper has increased, together with the need for drainage aids. The resins of the present invention differ in having a polyamine/diacid mole ratio between 1.5 and 2.0 to 1.
U.S. Pat. Nos. 2,926,116 and 2,926,154, both to G. I. Keim, describe poly(aminoamides) from polyalkylenepolyamines and dicarboxylic acids, with polyamine/diacid mole ratio between ca. 0.8 and ca. 1,4 to 1. These are alkylated and cross-linked with epichlorohydrin, at an epichlorohydrin/secondary amine mole ratio between 0.5 and 1.8 to 1.
U.S. Pat. No. 3,632,559 to M. Matter et al. describes aminopolyamides with adipic acid/polyalkylenepolyamine mole ratios between 0.85 & 1.2 [whence, amine/acid between 1.176 and 0.833]. These are cross-linked by precondensation products of x moles dimethylamine and x+l moles epichlorohydrin, having the formula: ##STR1## using low mole ratios of this cross-linker to secondary amine in the polyamide.
The prepolymers of Matter et al. must be polyamides, or oligoamides of at least five (polyamine-dibasic acid) repeat units; whereas, the amine/acid ratios of the resins of the present invention (where based on dicarboxylic acids) would give oligomers averaging not over two repeat units.
U.S. Pat. No. 3,891,589 to D. K. Ray-Chaudhuri discloses in column 2 polyamide-polyamine-epichlorohydrin resins in which the mole ratio of polyamine to carboxylic acid can range between 0.9 and 1.5 and the number of moles of epichlorohydrin per equivalent weight of polyamide-polyamine intermediate can range from 1.25 to 4.0. At a polyamine/dicarboxylic acid ratio of 1.5 (=3:2), the average molecule will contain 3 polyamine moieties and 2 acid moieties. This may be viewed as "two repeat units plus an extra polyamine end-group", or as having three of the secondary amines that characterize a repeat unit. At a polyamine/diacid mole ratio of 1.5/1, the resins of the present invention contain between 0.75 and 1.2 moles of bifunctional crosslinking agent per repeat unit of oligoamine precursor, or between 0.50 and 0.83 mole of linking agent per secondary amine equivalent.